Surprises and anomalies in acoustical and optical scattering and radiation forces

- Aspects of acoustical and optical radiation forces and torques and scattering theory reviewed.
- From geometric considerations radiation forces on objects in beams may be negative.
- An extinction theorem is noted for objects in an invariant beam like a Bessel beam.
- Diffraction catastrophes of spheroidal drops and anomalies for bubbles reviewed.
- Various acoustic elastic and caustic-related scattering enhancements reviewed.

Experiments on radiation torques and negative radiation forces by various researchers display how the underlying wave-field geometry influences radiation forces. Other situations strongly influenced by wave-field geometry include high-order caustics present in light-scattering patterns of objects as simple as oblate drops of water or oblate bubbles of air in water. Related theoretical and experimental investigations are considered. Acoustic scattering enhancements associated with various guided waves are also examined. These include guided waves having negative group velocities and guided wave radiating wavefronts having a vanishing Gaussian curvature.